Glycosides are chemical substances wherein a saccharide is bonded to a non-saccharide part called aglycon, and are widely present in nature.
Some glycosides are known to exhibit physiological activity through decomposition into aglycons by a glycosidase such as glucosidase produced by enteric bacteria though the glycosides themselves do not exhibit the physiological activity because of their poor enteric absorption, as phytochemicals (phytogenic functional ingredients) such as polyphenols having antioxidation action and phytoestrogens having a weak estrogenic action. Thus, in view of preventing and symptom-alleviating effects of life-style related diseases such as cancer, arteriosclerosis, osteoporosis, and climacteric disorder, and diseases owing to aging, attention has been focused on soybean protein concentrates, soybean-processed materials, and food containing the soybean protein concentrates.
Among the phytochemicals, glucosides that contain isoflavones as aglycons as represented by the following general formula (hereinafter, sometimes referred to as isoflavone glucosides) contain aglycons such as daidzein, genistein, glycitein, and it is revealed from cellular level investigations and epidemiological surveys that they inhibit growth of breast cancer and prostatic cancer cells, alleviate arteriosclerosis and osteoporosis, and also alleviate climacteric disorder owing to the female hormone-like estrogenic action.
(wherein R1 and R2 each is independently selected from the group consisting of H, OH, and OCH3, and R3 is selected from the group of H, COCH3, COCH2COOH, and COCH2CH2COOH)
However, there is a possibility that a sufficient amount of glycosidase cannot be produced by enteric bacteria in elderly persons, sick persons, and antibiotics-administered patients, and also a glycosidase is difficult to decompose glycosides modified with acetyl or malonyl group and disaccharide or trisaccharide glycosides, so that it cannot be expected to absorb a sufficient amount of phytochemicals contained in soybean protein concentrates and the like.
Moreover, it is avoided to take foods containing soybean-processed materials such as soybean protein concentrates especially in Western countries owing to the distinctive smell and bitterness, and thus some limitation exists as sources of aglycon isoflavones.
Accordingly, a process for forming phytochemicals efficiently in a living body, and an improvement of flavor of a soybean-processed material rich in aglycon isoflavones, which are highly efficiently absorbed and capable of ingesting a sufficient amount of isoflavones by taking small amount of them, and having less smell and bitterness distinctive of soybean or of a food containing the soybean-processed material have been desired.
On the other hand, the method for converting an isoflavone glucoside into an aglycon isoflavone is known as described in JP-A-10-117792. In this method, a phytogenic protein extract is treated with an alkali to convert a modified glucoside isoflavone into a glucoside isoflavone, which is then subjected to a treatment with glycosidase. Such a treatment is carried out because conventional glycosidase cannot act directly on the modified glucoside isoflavone. Thus, the method is accompanied by the problems of requirement of two steps, enhancement of bitterness by the alkali-treatment, change in physical properties and ingredients, formation of by-products, waste liquid after the alkali-treatment, and the like. Also, glucosidase which takes charge of a main part of the action tends to be influenced by free glucose, so that the kind and concentration of the material used for the production may be limited.
Moreover, JP-A-8-214787 describes a process for converting a glucoside isoflavone into an aglycon isoflavone by fermentation using a microorganism. However, there are possibilities of decomposing the resulting aglycon isoflavone by the microorganism and of forming unexpected by-products, and therefore many problems may arise at the actual production.
Furthermore, a method of hydrolysis with an acid such as hydrochloric acid may be a candidate, but the decomposition of proteins, phospholipids, neutral lipids, and other ingredients may occur along with formation of by-products because of the severe conditions. Especially, the formation of chlorinated compounds such as MCP (monochloropropanol) and DCP (dichloropropanol) whose carcinogenicity has been reported cannot be avoided.
Therefore, an object of the invention is to provide a process for producing a phytogenic physiologically active substance of aglycon type efficiently without resort of any acid/alkali treatment or fermentation and substantially without changing the physical properties of a material. Moreover, other objects of the invention are to enhance the aglycon content in a protein or a protein-containing food by using diglycosidase and/or a specific enzyme preparation and to improve the flavor. These objects and other objects will be further clarified by the following detailed explanations.